Table of contents

This special issue of Nanotechnology contains papers selected from four symposia of the 8th International Union of Materials Research Society Conference on Electronic Materials (IUMRS–ICEM 2002), which was held in Xi'an, China, 10–14 June 2002. The four symposia are Symposium C: Materials and technologies for Electronic and Optoelectronic Devices, Symposium E: Molecular and Biomolecular Electronics, Symposium I: Spintronics: Materials and Applications, and Symposium J: Advanced Materials and Technologies for Data Storage and Nanoelectronic Devices. They covered recent progress on nanodevices and advanced materials, including nanoelectronics, spintronics and moletronics. A wide diversity of scientific disciplines were represented, as seen in the selected papers in this issue.

Sixteen symposia, including six plenary lectures, were held at the IUMRS–ICEM 2002 conference. In the four symposia mentioned above, 239 papers were presented. Ninety-two of the submitted papers (including 25 invited talks) were accepted for publication after the peer-review process. Fifteen of them are presented in this special issue of Nanotechnology, and the rest will be published in an accompanying IOP Conference Series book.

The success of IUMRS–ICEM 2002 was due to the contributions of many individuals. We would like to thank all the referees for their constructive and critical reviewing work. We are particularly indebted to the C-MRS, the Conference Chair, and the Chairs of the four symposia, Professors Zhanguo Wang, Meixiang Wan, Yunqi Liu, Wuyan Lai, Zhaohuan Chen, and Zhongfan Liu. We would also like to thank the people from the Nanoscale Physics and Devices Laboratory, Chinese Academy of Sciences, for their work on the proceedings. Special thanks should go to Dr Hongwen Liu and Mr Xiao Lin for their help with the preparation of papers.

Guest EditorsHongjun GaoHarald FuchsDongmin Chen

Ordering of lateral semiconductor nanostructures, quantum wires and quantum dots, is the prerequisite for exploiting their unique electronic properties in novel quantum functional optical devices. We present our approach based on the generation of periodic step arrays on shallow mesa-patterned GaAs(311)A and (100) substrates by molecular beam epitaxy. Pattern-induced step arrays locally modify and modulate the surfaces structural and chemical properties generating unique templates for further ordered nanostructured materials growth. This is based on the evolution of different types of step arrays depending on surface orientation and mesa direction and is demonstrated for the case of (In, Ga)As island formation.

Modification of electron density in the surface states of Au(111) and Cu(111) surfaces by Pd deposition is demonstrated. Using a low-temperature scanning tunnelling microscope, electronic standing wave patterns are observed on a monolayer-high Pd layer whose wavelength is longer than that of the substrates. The observation indicates an upward shift of the energy level of the surface states and reduced electron density in the states on the overlayer. A standing wave pattern depending on magnetic field was observed around an impurity atom on the Au(111) surface.

The nucleation and growth of Si and Ge clusters/crystallites on SiN_x films, which act as relative inert substrates, proceed in a quite complicated manner compared with conventional epitaxial processes. We examine the size dependence of the shape, surface structures and orientation of nano-scale clusters/crystallites. Facets are not observed until the crystallite diameter reaches ∼40 nm. Due to the isotropic surface energy and a weak interaction with the substrate, the orientation of the clusters/crystallites is random initially. A preferred orientation, however, emerges on crystalline SiN_x films as the crystallite size increases. The growth nature of nano-particles, their interactions with the substrates and among themselves determine the overlayer texture as the amount of material deposition increases.

Various perpendicular ferromagnetic superlattices of the Co/Pd system were made to tune magnetic properties and recording performance, dependent on factors like sputtering pressure, sputtering gas, bilayer number, sublayer thickness, deposition temperature, annealing, type of seed layer, seed layer thickness and grain size, and distribution. Structural analysis by x-ray diffraction and TEM shows columnar growth and orthorhombic (tetragonal) microcrystalline packing that accounts for the ferromagnetic properties by polarization of the atoms during deposition, in contrast to the non-ferromagnetic state of the fcc crystal structure superlattice after high-temperature annealing. The M–H loop is described by a recently developed analytical hysteresis model and the result is substantiated by the structural analysis of grain sizes from multiple magnetic phases.

An assembly of Au nanoparticles is fabricated by the condensation of peptide bonds between L-lysine molecules attached to the surface of 13 nm Au nanoparticles. The formation of peptide bonds between the L-lysine molecules is confirmed by Raman spectra. It is found that L-lysine molecules are absorbed onto the Au colloid surface via the interactions between the ε-amino group of L-lysine and the Au colloid. UV–visible spectral measurements show there are strong interactions between the Au nanoparticles linked by dipeptides (lysine–lysine) in the self-assembly. Transmission electron microscopy observations show that the distance between two adjacent nanoparticles is about 1.5 nm, which is consistent with the calculated length of the dipeptide.

The self-assembly of Si on the dimer vacancy array (DVA) is studied. Factors, such as the amount of deposition, substrate temperature and annealing temperature, which affect the self-assembly processes are discussed. The formation mechanism of the DVA is discussed.

An organic thin film of N, N-dimethyl-N'(3-nitrobenzylidene)-p-phenylenediamine with electrical bistability properties was prepared by the vacuum deposition method. The film was observed with a scanning tunnelling microscope (STM). Ultrahigh-density data storage is demonstrated on the organic film, produced by applying a voltage pulse between the STM tip and the substrate of the thin film under ambient conditions. The average size of the recording marks is about 0.7 nm, corresponding to a data storage density of about 10¹³ bits cm⁻². The local current–voltage curves of the film suggest that the recorded area is conductive, while the unrecorded region possesses high resistance. The recording mechanism is also discussed.

Perfectly ordered arrays of identical Al and Ga clusters of nanometre size and spacing were spontaneously obtained using a novel technique, in which surface-mediated magic clustering is used to achieve the identical cluster size while the Si(111)-7 × 7 surface is used as a template for positioning the clusters in order. The atomic structures, formation mechanism and stability of the nanoclusters were studied with in situ scanning tunnelling microscopy combined with first-principles total energy calculations. The very high stability of these nanocluster arrays provides unprecedented opportunities for exploring new physical phenomena and great potential in technological applications.

An organic reagent-assisted method has been developed for the synthesis and assembly of copper sulfide, cadmium sulfide and silver sulfide nanocrystallites at low temperature under hydro- or solvothermal conditions. Nanowire-like aggregates (with an average diameter of 120 nm and length of 2 μm) assembled by digenite phase copper sulfide nanoparticles, nanotube-like aggregates (with diameters ranging from 40 to 200 nm and lengths from 400 nm to 4 μm) and nanovesicle-like aggregates (with size ranging from 50 to 180 nm) assembled using djurleite phase copper sulfide nanoparticles have been obtained using triethylenediamine, tramethylethylenediamine and di-n-butylamine as the linking agents, respectively. A cetyltrimethyl-ammonium bromide-assisted solvothermal process with CdCl₂ and thiourea as the reactants and ethylenediamine as the solvent has been proposed to control the length of the CdS nanorods from 300 nm to 4.5 μm and construct novel CdS nanorod-based structures, including polydentate wire-like architectures and polydentate sphere-like architectures composed of dozens of CdS nanorods of 10 nm in width and 100 nm in length. A CH₃(CH₂)₁₁SH-template method has been adopted to realize the synthesis and the simultaneous assembly of silver sulfide nanocrystallites with AgNO₃ and Na₂S as reactants. By changing the reaction temperature and the dodecylthiol concentration, two-dimensional orthogonal and hexagonal-like ordered silver sulfide nanoparticle arrays and quasi-orthogonal silver sulfide nanorod arrays can be obtained. This organic reagent-assisted route is very simple and can be extended to the synthesis and assembly of other semiconductor sulfide nanocrystals.

We have employed the first-principles molecular dynamics method to study the stabilities and electronic properties of bismuth nanotubes. There are some stable bismuth nanotubes. The strain energies of Bi(n, n) nanotubes follow the classical 1/D² strain law. For small Bi(n, 0) nanotubes, the strain energies show a non-linear dependence on 1/D². Bismuth nanotubes are predicted to be semiconducting in both (n, n) and (n, 0) forms. For small-diameter bismuth nanotubes, the band structure varies strongly because of hybridizations. As the diameters are larger than 18 Å, the band gaps of both Bi(n, n) and Bi(n, 0) nanotubes approach 0.63 eV, corresponding to the band gap of a bismuth sheet at the Γ point. Thus bismuth nanotubes are seen as potential semiconductor nanomaterials for future nano-electronics applications.

Conducting nanotubes of polyaniline (PANI) about 80–180 nm in diameter were synthesized by a chemical template-free method in the presence of D-10-camphorsulfonic acid (D-CSA) as the dopant, and ammonium persulfate ((NH₄)₂S₂O₈) as the oxidant. The effect of synthetic conditions, such as the molar ratio of D-CSA to aniline (An), the concentration of D-CSA in the polymerization media, the reaction temperature and time, on the morphology and size as well as the electrical properties of the PANI–(D-CSA) was investigated. It was found that the above synthetic conditions, especially the molar ratio of D-CSA to An, strongly affected the morphology and formation probability of the resulting PANI. The micelles formed by D-CSA and anilinium cations act as the templates in the formation of PANI–(D-CSA) nanotubes.

This paper describes the in situ synthesis of oligonucleotide arrays on glass surfaces by using soft lithography. In this method, based on the standard phosphoramidite chemistry protocol, the coupling was achieved by the glass slide being printed with a set of polydimethylsiloxane (PDMS) microstamps, on which was spread nucleoside monomer and tetrazole mixed solution. The elastic characteristic of PDMS allowed it to make conformal contact with the glass slide in the printing coupling. With regard to the efficiency of the printing coupling, the hybridization microscope images of 20-mer oligonucleotide synthesized via the directly drip-dropped coupling and the contact coupling were compared; the fluorescence intensities of the two methods showed no significant differences. The coupling efficiency was also investigated via an end-labelled fluorescence nucleotide method and a stepwise yield of 97% was obtained. A high-quality, high spatial resolution and large-scale PDMS stamp, which was developed by integrating 168 different microstamps on one glass substrate for synthesizing oligonucleotide arrays. The stamp was modified to improve the surface wettability by plasma discharge treatments, so that microstamps could be used to fabricate oligonucleotide arrays. A motional printing head was developed to improve the contact effect of the glass slide with different microstamps. A higher boiling point solvent was used in the printing coupling to inhibit solvent volatilization and to maintain the consistency of reagents on different features of the microstamp. An effective method was used to eliminate residual reactive nucleosides on chips with small molecules containing a hydroxyl group. A specific oligonucleotide array of four probes both matched and mismatched with the target sequence was fabricated to identify the perfect match and mismatch sequences.

We give some perspectives on the possibilities for application of the bacteriorhodopsin (BR) molecule in the development of nanoelectronic devices in conjunction with photonic crystals—materials with inhibited photonic band. This involves the use of a single BR molecule by 'changing' the photon gradient formation with externally initiated electric fields, preserving the mechanisms of negative reverse communication, or the use of an intermolecular mechanism of photo transitions and dependence on the electric field. Greatly enhanced optical responses, linear and nonlinear, in metal nanocomposites and nanodiamond containing nanoscale surface features have been intensively studied in recent years. These results foreshadow fascinating possibilities for linear and nonlinear local spectroscopy of single molecules. Use of photonic crystals (at present the only technologically realized three-dimensional photonic crystals are the opal matrices) suggests the possible application of a number of physical phenomena.

We have studied the possibility of room temperature superconductivity and nanoscaled conducting systems by using self-assembled monolayers of the C₆₀ derivatives C₆₀–O–C₈SH (C₆₀-SAMs). In this study the C₆₀-SAMs were synthesized on Au ultrathin films. The films were prepared on MgO single-crystal substrates whose surfaces had clear step–terrace structures. The morphologies of the C₆₀-SAM/Au films synthesized were observed by atomic force microscopy and the resistivities of the films were studied.

Self-assembled polypyrrole (PPy) micro/nanotubes, whose diameters and room temperature conductivities were within the ranges of 50–2000 nm and 2–40 S cm⁻¹ respectively, were successfully synthesized by a chemical and electrochemical method in the presence of β-naphthalene sulfonic acid or p-toluenesulfonate acid as the dopant. By changing the polymerization method and conditions as well as dopant structures, one can control the morphology, size and electrical properties of the doped PPy. It was proposed that dopant micelles or pyrrole/dopant clusters act as templates in the formation of the micro/nanotubes.

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